Heat treating apparatus



Nov. 29, 1966 o. L. STEWART HEAT TREATING APPARATUS 4 Sheets-Sheet 1Original Filed Jan. 18, 1962 b n RR E T N mm m T T 2 1 m L m 0 M L. F Ma o 5 3 u m 1] fl fiT HHHH 40 mS 2. m I

I I/ a. O I 4 5 1966 o. L. STEWART 3,288,452

HEAT TREATING APPARATUS Original Filed Jan. 18, 1962 4 Sheets-Sheet 2mix-M INVENTOR.

ORALD L. STEWART ATTORNEYS 1-966 o. 1.. STEWART HEAT TREATING APPARATUS4 Sheets-Sheet 3 Original Filed Jan. 18, 1962 mow mmm

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ORALD L. STEWART M mfvm/ ATTORNEYS NOV. 29, 1966 STEWART 3,288,452

HEAT TREATING APPARATUS Original Filed Jan. 18, 1962 4 Sheets-$heet 4 7Onov AC.

HIGH LIMIT O00 ZONE2 ZONEI IE1 D INVENTOR. QRALD L. STEWART FIG. 6 BYATTORNEYS United States Patent 3,288,452 HEAT TREATING APPARATUS Orald1L. Stewart, Rocky River, Ohio, assignor, by mesne assignments, toTextron, Inc., Providence, R.I., a corporation of Rhode Island Originalapplication Jan. 18, 1962, Ser. No. 167,021, now Patent No. 3,201,289,dated Aug. 17, 1965. Divided and this application July 20, 1964, Ser.No. 389,814 6 Claims. (Cl. 2664) This is a division of applicationSerial No. 167,021, filed J an. 18, 1962 and now Patent No. 3,201,289,issued Aug. 17, 1965.

This invention concerns a heat treating apparatus, particularly adaptedfor use in the heat treating of metal abrasive shot.

A novel apparatus combination is provided for performing the heattreating method and includes housing means, heating means for automaticcontrol of the temperature within said housing means, retort meansextending through said housing means and having a smooth cylindricalbore, cap means at either end of said bore substantially closing saidretort means, drive means imparting rotational movement to said retortmeans, EUUtO- matic feed means supplying said retort means with metalparticles adjacent one end of the cylindrical bore, and automaticdischarge means dispensing said metal particles into a quenching bathfrom said retort adjacent the other end of said cylindrical bore on asubstantially first-in, first-out basis.

The furnace of this invention is adapted especially to heat small metalparticles to any temperature up to approximately 2,000 F. on acontinuous flow basis at various rates, depending on the temperature.For example, in one form and size it can heat 2,500 pounds of steel shotper hour to a temperature of 1700 F. The furnace of the invention has amultitude of advantages not found in metal abrasive shot heat treatingapparatus of the type heretofore known in the shot producing industry,which result in low initial cost, low operating cost, and lowmaintenance cost.

Rotary retort furnaces of the general type herein disclosed are not new.In fact, their use in calcining processes is rather well known; however,the novelty and advantages of a furnace constructed according to theprinciples of this invention for heat treating metal abrasive shot, liesin its efficient retort design, mechanical drive design, and control setup, all of which cooperate to make possible a continuous metal shot heattreating process of extreme efficiency which requires a minimum ofmanual labor and supervision. The known prior art rotary furnaces forheat treating metal have contained ribbed spirals and uneven sections inthe retort which produce excessive stresses in the structure or theretort as its temperature changes. These spirals and uneven sections areboth diflicult and expensive to cast or fabricate and cause rapidfatigue of the metal retort and its eventual cracking during use.Moreover, the spirals and uneven sections conventionally used in rotaryretorts provide obstruct-ions which tend to induce sticking or weldingof the heated metal particles to the inside surface of the retort, thusgreatly increasing the number of retort cleanings required.

In the prior art apparatus for heat treating metal abrasive shot it hasbeen necessary conventionally to provide some type of positive workdriving or propelling means, such :as internal retort flights, vibratingchutes, or batch type baskets and trays, to move the metal abrasiveparticles into and out of the furnace. The use of these expensive priorart propelling means has resulted in high replacement and maintenancecosts which are attributable in a large measure to the sticking of thehot metal particles to the propelilng means within the retort.

The prior art has relied upon the use of expensive and complicatedcontrolled atmosphere systems, to minimize the metal abrasive particlesticking within the retorts, which have been characterized by theprovision of elaborate sealing structures and control apparatus. Thecompact furnace of the instant invention, by eliminating the need formetal abrasive particle propelling means and using a smooth bored retorthas eliminated substantial particle sticking and the need for the priorart type of controlled atmosphere and sealing means in heat treatingmetal abrasive shot and, therefore, has reduced both the manufacturingand maintenance costs of the furance while increasing the capacitythereof. It is possible, however, that for use in metallurgicalprocesses, such as carburizing the case hardening, the furnace of thisinvention can be converted easily for efiicient use with specialatmospheres in view of the substantially closed retort means utilized.

Other prior art problems which traditionally have been encountered inrotary retort apparatus are those caused by heat tansfer from the retortto the elements in the drive mechanism for rotating the retort. Heattransfer to these parts has resulted in high maintenance costs due tothe fact that the heat softens and weakens the metal and thereby causeswear .and distortion which results in misalignment of wheels, damage tobearings, and fatigue of gear and chain elements.

The prior art feeding and control apparatus for rotary retort furnaceshas been elaborate and inefficient and has not safeguarded adequatelythe quality of the products being treated therein. With the increaseddemands of industry for high quality metal abrasive shot material, therehas been a constant problem of volume production due to the heattreating necessary to maintain uniform high quality shot. The continuousheat treating furnace provided by the principles of this invention isadapted particularly for solving the foregoing problems in a moreefi'icient manner than was heretofore thought possible.

It is, therefore, the general object of the invention to provide animproved apparatus useful in connection with the continuous heattreating of metal abrasive shot.

It is a more specific object to provide a heat treating furnace formetal abrasive shot which automatically controls, feeds and dischargesthe shot into a quench bath with a minimum of human attention and amaximum of high quality uniformity.

Other and more specific objects of the invention will be apparent fromthe drawings and the detailed description to follow:

In the drawings:

FIG. 1 is a side elevation view with certain of the parts broken away toillustrate one form of furnace according to the principles of thisinvention;

FIG. 2 is an elevation view of the input end of the furnace of FIG. 1;

FIG. 3 is a cross-sectional view of the furnace along the line 33 ofFIG. 1;

FIG. 4 is an elevation view of the discharge end of the furnace;

FIG. 5 is a schematic side elevation view showing the furnace burnersand controls;

FIG. 6 is a wiring diagram of the furnace control means.

The specific furnace embodiment shown and described utilizes a two-zoneheat control system for the furnace combination; however, single ormultiple zone versions are contemplated. A single zone type of heatcontrol has been found to be successful but is slightly less efiicientthan the described two-zone system.

Referring now more particularly to the drawings, the apparatus of thisinvention comprises a furnace combination which includes housing means20, heating means 30, retort means 40, feed means 50, retort drive means60, electrical control means 70 (see FIG. 6), quenching means 80,conveyor means 90, and power transmission means 100.

As seen in FIGS. 1 and 3 of the drawings, the housing means of theillustrated furnace combination 10 is an elongated trough-shaped metalcasing 21 lined by a refractory brick structure 22 having a centralcavity 23 which is of a semi-circular cross-sectional shape in its lowerportion 24 and is of an enlarged irregular shape in its upper portion 25adjacent the heating means 30. The retort means 40 extends throughopenings 26 and 27 in the ends of housing means 20 and is supportedexternally for rotation therein about the axis of the semicircular lowerportion 24 to provide for the efficient distribution of heat within thecavity 23. Venting passageways 28 are disposed in the upper portion ofthe cavity 23 to permit removal of the combustion gases generated duringoperation of the furnace.

The heating means 30 includes conventional air-gas burners 35, such asthe type produced and sold by North American Manufacturing Company of4455 East 71st Street, Cleveland 5, Ohio, under the designation ofSeries 4423-33. These burners include an observation port and combustiontile and are equipped with pilot tips for lighting. The burners aremounted in openings 29 in housing means 20 and are capable of closeregulation by varying automatically the air-gas supply thereto in amanner hereinafter to be described. Several different numbers ofburners, preferably from 4 to 12, may be used in the furnace dependingon the temperature requirements of the desired heat treating process.

For example, in the embodiment described herein a bank of six burnershas been found to be satisfactory for a wide range of applications. Whenoperated together with an air pressure of 8 psi, these six burners arecapable of producing 1,830,000 B.t.u. per hour from a 20 inch flame.

In geographic areas where electrical power rates are low, electricalheating means for the furnace could be substituted for the gas meansdescribed, or, as will be obvious further to those skilled in thecombustion art, a suitable oil combustion system also could be used ifdesired.

The retort means of the furnace 10 is a generally cylindrical metalcasting or fabrication, 41, of greater length than the housing means 20having a smooth central bore 42 therein. Cylinder 41 has an aperturedradially inwardly directed flange 41a welded or otherwise provided ateach end thereof for connection of the end structure thereto. Suitablefastening means, such as bolts 41b extend outwardly through flange 41ato secure apertured radially outwardly directed tire-like circularflanges and 46 to the ends of cylinder 41. The flanges or tires 45 and46 are retained in place on bolts 41b, concentric with cylinder 41, bysuitably apertured and centrally bored end caps 43 and 44 and nuts 41cthreadedly associated on the bolts extending through the alignedapertures of the members. Rotational motion is imparted to the retort byfrictional drive on the outer surfaces of the tires 45 and 46 in amanner to be explained later.

The described fastening arrangement for the end structure of cylinder 41is preferred, although other fastening means may be used in thecombination because of the convenienct of assembly and disassembly whichit affords. It has been found in this respect that by mounting the bolts41b close to the bore 42, as illustrated in FIG. 1, the tool pads on thebolt heads prevent rotation of the bolts relative to the aperturedmembers, and the nuts, therefore, may be threaded or unthreaded withouthaving to hold the bolts with a wrench or other means on the inside ofthe structure. A series of holes 49 opening radially through the wall ofthe retort cylinder 41 are spaced symmetrically around the peripherythereof adjacent the discharge end of the furnace outside of the housingmeans 20 for substantially continuous discharge of shot from therotating retort.

An automatic feed valve 50 for introducing metal shot particles into thebore 42 of the retort 40 is connected to be responsive to the furnacewhen it is operating. The valve 50 is mounted adjacent a funnel 51 andwhen the valve 50 is open shot flows into the funnel and through apassageway 52 connected thereto, past the hole 48 of the end cap 43,into the retort bore 42. The particles then flow along the rotatingsmooth bore 42 in a manner analogous to the flow of a liquid until theyare discharged on a first-in, first-out basis through the ports 49 intoa quenching or cooling medium.

The retort cylinder 41, which is produced either by casting orfabricating, is preferably of heat-resistant highalloy steel. Theuniform cross section of the retort wall and the smooth bore 42 providea uniform cross section which prevents excessive thermal stresses frombuilding up as the temperature of the retort changes. These stresses, ifnot reduced in this manner, would cause rapid fatigue of the retort andeventual cracking. This provision greatly prolongs the life of theretort cylinder.

Another particular advantage of the retort is that the smooth finish ofbore 42 minimizes sticking of heated metal particles to the insidesurface. This significantly increases the operating time between retortcylinder cleanings and renders the use of controlled atmosphere in thefurnace unnecessary, thus greatly reducing cost. This sticking problemwith retorts for heating metal particles is a critical one becausematerials sticking to the inside of the retort results in poor heattransfer and consequently reduction in production. This is caused by theformation of a ring of metal from the shot particles with a differentexpansion rate than the retort itself, thus setting up higher stresses.The reason that the smooth bore type of retort can be used for heattreating shot is that the small metal particles behave as a liquid whenagitated by the rotating motion of the retort. This action causes theparticles to travel uniformly through the retort in a continuous flow asnew material is introduced on the feed end to displace material out ofthe discharge end outlet on a substantially firstin, first-out basis. Ofcourse, the retort cylinder can be used in other than a horizontalposition because of this action and it is possible to give the structurea slight tilt in either direction, but in order to avoid bearingoverloading in the drive mechanism or misalignin g the driving parts,the horizontal position is preferred.

According to the feed principles used in the furnace of this invention,a rotational motion must be imparted to the retort to effect uniformheating of the retort and to keep the metal particles progressingthrough the furnace. In the disclosed embodiment of the invention, arotation rate of 7 to 10 revolutions per minute has been found optimum;however, this may vary widely depending upon the particular heattreating procedure being used. The particular described shape of thecavity 23 of the housing means 20 is designed for optimum distributionof heat in the furnace and creates a circulation of air around therctort as shown by the arrows in FIG. 3.

The retort drive means 60 includes two longitudinal shafts 61 and 62mounted in pillow blocks 63 at either end axially outwardly from theretort tires 45 and 46. Adjacent the pillow blocks 63 on the feed end ofthe furnace are two flanged wheels 65 and 66 conventionally secured onthe shafts to rotate therewith. The flanges and wheel width are suchthat the tire 45 frictionally engages the inner surfaces of the flangedwheels 65 and 66 between the flanges. Similarly positioned on theopposite ends of the shafts 61 and 62 inside the pillow blocks 63, inalignment and supporting frictional engagement with the tire 46 are twounflanged wheels 67 and 68. This arrangement provides constant alignmentof the retort tire 45 with respect to the flanged wheels 65 and 66 andpermit thermal expansion of the retort to be taken up by the unfiangedwheels 67 and 68.

The wheels 65, 66, 67, and 68 are of rather massive construction with aradius determined by the heat transfer characteristics of the materialfrom which they are made, since it is imperative that a minimum of heatbe transferred to the shafts 61 and 62 and, of course, to the bearingsof pillow blocks 63. Moreover, the tires 45 and 46 of the retort means40 are large enough so that heat does not travel easily to wheels 65,66, 67, and 68. This keeps the temperature on the tire peripheries lowand results in longer life of both the tires and wheels. Also ofimportance to the life of the furnace is the fact that shafts 61 and 62are provided the full length of the furnace so that misalignment of thewheels which would cause rapid wear is eliminated. Moreover, thefrictional drive utilized eliminates the use of low speed-high torquegears or sprockets on the retort cylinder itself and exposure of thedrive means to heat which would result in high maintenance costs.

The shaft 61 and wheels 66 and 68 of the retort drive means 60 aredriven in any conventional manner by generally designated powertransmission means 100, illustrated in FIGS, 1 and 2 as electric gearmotor 101, having a driving sprocket 102 mounted on the shaft thereofand connected by means of chain 103 to a driven sprocket 104 rigidlymounted on shaft 61 by means of key 105. The means of driving shaft 61may be varied, of course, as by direct gearing, or 'by a shaft mountedgear head driven by a standard speed electric motor, if desired, and theillustrated power transmission means is provided merely as an example ofone practical form which power transmission means 100 may take.

The shaft 62 and the wheels 65 and 67 mounted thereon are idlers whichreceive their rotation from frictional engagement with the rotatingretort tires 45 and 46 and, therefore, need not be driven directly bypower transmission means 100 in the manner in which shaft 61 and wheels66 and 68 are driven. The idling shaft 62 does serve a function inaddition to supplying support for the rotating retort cylinder 41,however, in that a motion sensitive zero speed switch 76 is connectedthereto which, if the retort stops rotating for any reason, actuates analarm 75, as will be seen in FIG. 6.

As the power means 100 drives the shaft 61 and retort cylinder 41 andthe automatic feed valve 50 is actuated, the metal particles flowthrough the rotating retort cylinder 41 and are discharged through theports 49, as previously explained, into a quenching bath 80 positionedbelow the ports. The quenching bath for most metal abrasive shot is awater bath, but may, of course, be any conventional quenching medium,such as oil or the like, depending on the structure required. Alsodisposed in the quenching bath container 81 is a conventional means 90,preferably with dip buckets thereon which cooperate with a sloped floor82 of the bath container 81 to pick up the shot from the bottom of thebath 80 and remove it to a cool dryer or storage position. Thus, thefurnace is set up to heat treat and quench metal abrasive shot withoutthe attention of a full time attendant.

A control means 70 is provided which alerts responsible persons in theplant to any abnormal condition in the apparatus and an alarm sounds ifany of the following things occur:

If the temperature drops below a desired low limit as indicated by thevarious thermocouples 71, such as the One projecting into the retortcylinder 41 through the bore 47 of the end cap 44.

If the furnace temperature rises a predetermined amount above theoperating range;

If the retort stops rotating;

If the fuel or air supply fails.

The feed valve 50 preferably is a pneumatically operated type dippervalve connected in the control circuit 70 such that when the first ofthe aforementioned abnormal conditions occur, the feed of the metalparticles to the furnace is stopped. This helps to insure the product isnot produced when the furnace is not operating correctly. Thepneumatically operated dipper valve 50 controls the feed rate into thefurnace accurately by means of a manually movable stop which limits theopening of the feed gate.

FIGS. 5 and 6 relate to the combustion and control systems of thedescribed furnace and are set forth herein only by way of an example ofone practical embodiment of the heating means 30 and the control means70 which may be used in connection 'with the invention.

The gas combustion system 30 schematically illustrated in FIG. 5 isdivided into two zones for accurate temperature control within thefurnace. The first zone is the preheat zone and the second zone is themaximum temperature zone. The first zone includes the three burners tothe left or feed end of the furnace and the second zone includes thethree burners to the right or discharge end of the furnace.

The gas supply line 31 has connected therein a manually actuable maingas cock 201 with a limit switch connected in control circuit 70 whichshut-s off and opens the supply of gas to the furnace. A gas pressureregulator 202 of the conventional diaphragm type keeps the gas pressureto the furnace constant as the main line pressure varies from seasonalor other causes. A safety shut-off valve 203 is connected electricallyin the control circuit 70 to shut off the gas supply from line 31 whenthe power fails; the gas pressure drops too low to give propercombustion; the air supply fails; or, the furnace overheats. The valve203 also may be used to keep the gas ofi until all the burner gas cocksare closed for individual opening and lighting. Its connection in thesystem will be readily apparent from the drawings and the description tofollow.

A low gas pressure switch 204 actuates the safety shutoff valve 203through the circuit 70 if the gas pressure from the gas supply line 31drops too low. A control of the air-gas ratio is provided by aconventional diaphragm regulator mechanism 205 connected between gassupply line 31 and air supply line 32 and this control assures that aproper gas-air ratio is provided to all of the burners as the air'pressure is changed in the line 32.

The zone one burners are normally on high fire at all times duringoperation of the furnace and a solenoid gas valve 206 connected incircuit 70 is provided in the zone one branch 33 of gas supply line 31,to control the flow of gas to the Zone one burners. If the controlcircuit 70 registers an excess of heat in zone one, the solenoid valve206 shuts off and the low fire bypass valve 207 provides a restrictedgas supply to the burners. The magnitude of the zone one low fire gassupply in such that it is preset by the valve 207 to a level which iscombined with the line 33 gas flow to give the proper high fire gassupply during normal operation. The gas pressure gauge 208 is used tocheck the pressure in line 33. A similar gas pressure gauge 208 ismounted in the zone two branch 34 of the gas supply line 31. Wherecloser control is desired, zone one is provided with a ratio controlsystem the same as in zone two.

The burners 35 of the combustion system 30 are separated from theirrespective branch gas supply lines by conventional manually operablesafety gas valves 209 which are interconnected by check line 36 throughsafety air passages which must be opened before the safety valve 203 canbe opened. To assure that all of the valves 209 are closed, a checkingair pressure switch 210 is connected in the line 36 which prevents theoperation of valve 203 until the valves 209 have been closed. Alsoprovided between thebranch zone supply lines 33 and 34 and the burners35 are limiting orifice gas valves 211 for adjusting the flow of gas toeach individual burner.

The pilot system for the burners 3.5 is supplied by a gas line 37connected to the main gas line 31. The line 37 has therein aconventional atmospheric type pressure regulator 213 and a manuallyoperable on-off valve 214 for simultaneously shutting off and openingthe gas line to all the pilots. A pilot air supply line 38 is connectedto the main air supply line 32 and is connected with the line 37 to apilot mixer 215 which mixes the gas and air for all the pilot tips 216.The gas-air mixture is conducted through pilot supply line 39 to theindividual pilot tips 216. The gas burners 35 have observation ports 217located thereon to facilitate their adjustment to the proper flamelevel.

The air pressure for the combustion system is supplied to the main airsupply line 32 by a conventional combustion air blower 218. The airsupply to the zone two portion of line 32 is regulated by a poweroperated butterfly air valve 219 which is controlled by the circuit 70to be opened at any of three positions depending on the temperaturewithin the zone. The air pressure within the zone may be observed bymeans of a conventional gauge or manometer 221.

The air supply to the individual burners 35 is adjusted manually bybutterfly air valves 222 in the lines between the main air supply line32 and the burners 35. If the air pressure gets too low for safeoperation, an air pressure switch 223 connected in the control circuit70 shuts off the gas safety valve 203.

FIG. 6 is a circuit diagram schematically showing the wiring of the 110volt control circuit 70 which actuatcs the various mechanisms of thecombustion system described in connection with FIG. 5. The power circuitwhich supplies the current for the motor 100, the blower 218, and theconveyor 90 is conventional and is not illustrated.

The control circuit 70 is provided with automatic alarm 75 which may beset by switch 77 to sound off whenever any of the abnormal conditionspreviously listed occur. In addition, indicator lights 78 are providedto show the condition of the key control system elements at any giventime. They are used also as a means of determining the source ofabnormal conditions.

A switch 201s is provided on manually operable main gas valve 201 toindicate the open-shut position of the valve by means of a light 78 inthe control circuit 70. A main electrical switch 74 is provided in thecircuit 70 to shut olf the power to the remainder of the controlcircuit.

With the switch 74 closed the control circuit acts such that thepressure switches 204 and 210 are closed as long as proper pressuresthrough them are maintained as explained in connection with FIG. 5.Also, normally open safety valve relay 203r, underheat relay 30r, andretort stopped relay 40r, .are connected in the alarm circuit such thatif any of the thermocouples 71 indicate an abnormal temperaturecondition through conventional controllers A and C (such as sold byMinneapolis-Honeywell Regulator Co., Penn and Bay Streets, Fall River,Mass., under the designation Pyr-O-Vane models 105 and 106), or the zerospeed switch indicates that rotation of the retort has stopped, thealarm is sounded, and, depending on the nature of the trouble, thesafety shut-01f valve may be closed. Further provision in the circuit bymeans of feed switch 79 in connection with the electropneumatic feedvalve 50 automatically shuts off feed of shot to the furnace in theevent of an abnormal condition.

Thetwo zone control system of the illustrated embodiment is providedsuch that the gas supply to the zone one burners is controlled by valves206 and 207. If the thermocouple 71 in zone one, connected in circuit 70by means of conventional control and amplifying means A, senses that thetemperature within the zone is below 1300 F., the solenoid gas valve 206is opened and the burners in the zone are placed on high fire. If thetemperature in zone one exceeds 1300 F., the solenoid closes the valve206 and the low fire bypass which has been preset by gas 207 is the solesupply of gas for these burners until the temperature drops below 1300F., and the valve 206 again opens. The burners can be adjusted so thatthis zone levels off at about 1295" F. and remains on high fire.

The air supply valve 219 to zone two is actuated similarly by athermocouple connected by means of conventional control and amplifyingmeans B (such as sold by Minneapolis-Honeywell Regulator Co., BrownInstruments Division, Philadelphia, Pa., under the designationElectroniK l7 Controller) in circuit 70 such that by means of theair-gas ratio control means 205, the air is kept in constant ratio tothe gas supply and the valve 219 is wide open at 1690 F.; at 1695 F.valve 219 is approximately two-thirds open; at 1700 F., valve 219 isone-eighth open. If the temperature in zone two is below 1680 F., thecontrol circuit 70 insures that the feed is shutoff at the feed valve50. A high limit thermocouple 71 has a high limit safety shut-downcontrol and amplifying means C which shuts off the safety shut-off valve203 in the event the temperature exceeds 1950 F. in the furnace.

Accordingly, the heat treating of metal abrasive shot according to theprinciples of this invention begins with bringing the furnace up totemperature so that the controls of circuit 70 will maintain thetemperature automatically. As the metal particles are fed automaticallythrough the feed valve 50 and arrange themselves into substantiallycontinuous paths over a substantial length of the rotating retort, adischarging of the metal particles from the ports 49 into the quenchingbath occurs on a substantially first-in, first-out basis. The conveyorremoves the heat treated metal shot from the bath 80 to complete theoperation.

For ease of description, the principles of the invention have been setforth in connection with but a single illustrated embodiment thereof. Itis not my intention, however, that the illustrated embodiment nor theterminology employed in describing it, be limiting inasmuch asvariations may be made without departing from the spirit of theinvention. Rather, I desire to be restricte only by the scope of theappended claims. 1

The invention claimed is:

1. A heat treating furnace for metal particles comprising housing means,heating means mounted on said housing means including separate controlmeans for a preheating zone and a high temperature heat-treatment zone,retort means extending through said housing means and having a smoothcylindrical bore, cap means at either end of said bore substantiallyclosing said retort means, friction drive means imparting rotationalmovement to said retort means, automatic feed means electricallyinterconnected with said control means for supplying said retort meanswith metal particles adjacent one end of the cylindrical bore when saidheating means and drive means are in operation, automatic dischargemeans dispensing said metal particles from said retort adjacent theother end of said cylindrical bore on a substantially first-in,first-out basis into a quenching medium.

2. A heat treating furnace for metal particles comprising arefractory-lined housing means of irregular internal shape, zonecontrolled heating means controlling the temperature within said housingmeans, metal retort means extending through said housing means andhaving a smooth cylindrical bore, cap means secured to either end ofsaid bore substantially closing said retort means, friction drive meansimparting rotational movement to said retort means through means mountedon the ends thereof, feed means supplying said retort means with metalparticles adjacent one end of said cylindrical bore, spaced PQIWWS inthe Wall of said retort means dispensing said metal particles from saidretort adjacent the other end of said cylindrical bore on asubstantially first-in, first-out basis.

3. The furnace structure of claim 2 in which the friction drive meansincludes parallel shafts mounted with the ends thereof in supportbearings, massive Wheels mounted on each end of said shafts adjacent thesupport bearings, flanges on one pair of adjacent massive wheels on oneend of said structure, and in which said friction drive means includesmeans mounted on the retort ends and which are seated on the wheelsurfaces of said massive wheels between said flanges and the wheelsurfaces of said second pair of adjacent wheels at the other end of saidstructure, and means imparting rotational movement to one of said shaftssuch that said means mounted on said retort ends are frictionally drivenby the wheels of said one shaft and the wheels of said other shaft actas supporting idlers.

4. The structure of claim 2 in which an electrical alarm means isprovided which is actuated if the controlled zone temperatures dropbelow their respective desired low limit, if the controlled zonetemperatures rise .a predetermined References Cited by the ExaminerUNITED STATES PATENTS 1,656,924 1/1928 Smith 2664 X 2,182,616 12/1939Juthe 266-5 3,068,091 12/1962 Kirkland 263-32 X JOHN F. CAMPBELL,Primary Examiner.

J. M. ROMANOHIK, Assistant Examiner.

1. A HEAT TREATING FURNACE FOR METAL PARTICLES COMPRISING HOUSING MEANS,HEATING MEANS MOUNTED ON SAID HOUSING MEANS INCLUDING SEPARATE CONTROLMEANS FOR A PREHEATING ZONE AND A HIGH TEMPERATURE HEAT-TREATMENT ZONE,RETORT MEANS EXTENDING THROUGH SAID HOUSING MEANS AND HAVING A SMOOTHCYLINDRICAL BORE, CAP MEANS AT EITHER END OF SAID BORE SUBSTANTIALLYCLOSING SAID RETORT MEANS, FRICTION DRIVE MEANS IMPARTING ROTATIONALMOVEMENT TO SAID RETORT MEANS, AUTOMATIC FEED MEANS ELECTRICALLYINTERCONNECTED WITH SAID CONTROL MEANS FOR SUPPLYING SAID RETORT MEANSWITH METAL PARTICLES ADJACENT ONE END OF THE CYLINDRICAL BORE WHEN SAIDHEATING MEANS AND DRIVE MEANS ARE IN OPERATION, AUTOMATIC DISCHARGEMEANS DISPENSING SAID METAL PARTICLES FROM SAID RETORT ADJACENT THEOTHER END OF SAID CYLINDRICAL BORE ON A SUBSTANTIALLY FIRST-IN,FIRST-OUT BASIS INTO A QUENCHING MEDIUM.